Producing metals



E. EDWlN PRODUCING METALS @cit, 4, 1938.

Filed May 25, 1957 Wastegas Caa/ dust L imes [on 6 Hot gas M'x/hg vasse/vesse/ /Pea ch'on Ca C03 Ma ne/Ia separaior' mw E Y E. Edwin prvpme/orPatented Oct. 4, 1938 UNITED STATES PATENT QFFICE In Norway June 17Claims.

My invention relates to recovery of metals by direct reduction of theirores.

As is well known the question of direct reduction of oxydic and also ofsulphidic ores at low temperatures for recovery of the metal contentthereof has been studied for years, and much extensive research work hasbeen made in connection therewith.

In spite of this fact no method has hitherto been developed, which hasproved successful on a commercial scale. The main reasons for thisfailure are the following:

(1) It is extremely difflcult to supply the reaction energy necessaryfor the reduction in such manner that no overheating with bad attendingphenomena occurs.

(2) Most ores have during the reduction process, irrespectively ofwhether the same .is effected by means of solid carbon or by means ofgas, a strong tendency to undergo structural changes, which arefrequently accompanied by a caking of the charge, which renders theaccomplishment of the process very difllcult.

For solving these difilculties it has hitherto been necessary to makeuse of so complicated apparatus, that a common introduction thereof inthe industry has not been ventured, although several methods on anexperimental scale have given promising results.

It is the object of my present invention to provide a process by whichthe above mentioned drawbacks are avoided.

My invention is based upon an entirely new principle and a reactionhitherto unknown, and it provides a very simple method needing apparatusso plain as have previously been considered unattainable.

My invention is based upon the very simple reaction formulae:

(A) 2MeO+C+CaO- 2Me+CaCO:+Q1 or (using gas as reducing agent) InEquation (B) the relation HzZCO is to be so chosen, that the heatliberated Q2 is sufliciently high to compensate for all heat losses tothe exterior and. to keep the reaction temperature at the necessaryvalue. In some cases (by combination of Equations (A) and (13)) :c or ymay theoretically take zero value, which means that either only CO oronly H2 is used. The water vapour formed may, at the partial pressuresprevailing, easily be condensed on the walls of the reaction vessel. Itis directly possible to combine the Equations (A) and (B). Thus, if thereaction according to (A) is not sufflciently exothermal, smallquantities of CO may be supplied to the reaction space in order toincrease the positive heat value, since the reaction according to (B) isexceedingly exothermal for all oxides which can be reduced by gas.

Further, in order to increase the exothermicity of my process, it is inmany cases possible to obtain still better results by supplying to thereaction vessel a little free oxygen, which will then react according tothe equation (C) C+Oz+Ca0- CaCOa+l38000 In the case of iron ores, forthe reduction of which the present invention is especially suitable,

As will be seen, the exothermity of this reaction is, indeed, sufilcientfor the efiectuation of the reduction, but not excessively high.However, by a consumption of only 8% more of lime and coal in accordancewith Reaction (C) the development of heat may be increased by more thanquite small quantities of free oxygen being supplied to the reactionchamber.

However, the reaction in question will in general not take the courseindicated by the equations cited above, or, more correctly stated, noreaction at all will take place under normal conditions.

At this place the novel conception of my in- .vention comes in. Below Iwill explain this fully,

considering. by way of example the reduction of iron ores.

If a mixture of iron ore, lime and coal is heated in an open vessel toan initial temperature of, say, 800 C., and is then left alone, withoutfurther energy being supplied thereto, some small reaction will, indeed,at first occur between ore and coal. After a short period of timehowever such reaction will stop by itself, even if no losses of heat tothe exterior occur, as the charge very soon becomes so much cooled, thatthe temperature thereof goes below any usable reaction temperature.

Entirely different the result will be, if the above mentioned mixture isplaced in a closed, well insulated pressure vessel and is then heated tothe same initial temperature. Very soon a gas atmosphere, chieflyconsisting of carbon monoxide (CO) "and carbon dioxide (CO2) having asubteht1ally raised pressure will then occur in the said closed vessel,and under these conditions the reactions really take the courseindicated by the Equations (A), (B) and (C) cited above, such reactionsrunning quantitatively or substantially quantitatively from left toright in the sense of said equations. If an iron ore of normalreductibllity is treated in this manner, a pressure of 25-30 atmospheresvery soon is obtained, and the reaction then proceeds, the carbondioxide formed being absorbed by the lime present. The energy herebydisengaged is by radiation and conduction transferred to the reactionbetween coal and ore, and said reaction on its side develops furtherquantities of carbon dioxide and carbon monoxide, in a mutual relationdetermined by the reaction. To each temperature corresponds apredetermined pressure, and by artificially keeping the pressure at apredetermined value, a reaction temperature suitable for each charge inquestion may be maintained most exactly. If the heat losses to theexterior are higher than the exothermicity of reaction (A) this may atany time easily be compensated for by the reactions (B) or (C), asdescribed above.

In the drawing I have by way of example diagrammatically and flowsheet-like illustrated an arrangement for carrying out my method in thecase of iron ore being reduced by means of solid carbon as reducingagent.

Limestone is calcined in a lime kiln l, and a mixture of iron ore andcoal is preheated in a preheater 2. Preferably the waste gases from thelime kiln are utilized for heating said preheater. The hot lime from thekiln I and the mixture from the preheater are then taken to a mixingvessel 3 of any suitable construction, in which the lime, ore and coalare mixed. From this mixer the reaction mixture is by means of atransfer vat 4 transferred to the reaction vessel 5, in which thereduction of the ore takes place in the manner already described. Themixture of iron and limestone hereby formed is then taken to a coolingdrum 6, and after sufficient cooling the iron sponge is separated fromthe limestone on a magnetic separator I. The limestone hereby separatedout is in part returned to the lime kiln.

If free oxygen is to be supplied to the reaction vessel, in order to actin accordance with Equation (C), such oxygen must be supplied at thenecessary pressure, obtained by a compressor indicated at 8.

The reaction vessel may have any suitable shape, and is preferablyprovided with a gas inlet pipe and a gas blow off pipe (not shown). Thelatter also may be provided with a blow ofl' safety valve, in order thatthe pressure and temperature shall not be able to rise above the desiredvalue.

In order that the charge shall in no way cake together during thereduction operation, 'it is preferable to keep the reaction vesselslowly moving, say rotating. Such movement also furthers the exchange ofenergy between the reaction components.

Principally my method has been developed for the treatment of oxydicores; however in certain cases the method may as well be used forsulphidic ores, since the reactions proceed in accordance with lawswhich are entirely similar to those of the oxides.

What I claim is:

1. A method of producing metals from their ores, in which the ore isheated in the presence of a reducing agent containing the element carbonand of calcium oxide at such a pressure that carbon dioxide formed bythe reaction taking place is substantially quantitatively taken up bythe oxide of calcium under formation of carbonate of calcium.

2. A method according to claim 1, in which the reducing agent containsthe element carbon in combined form.

3. A method according to claim 1, in which the element carbon is used inthe form of carbon monoxide.

4. A method of producing metals from their ores, in which the ore isheated in the presence of a reducing agent containing the element carbonand a reducing agent containing the element hydrogen and of calciumoxide, at such a pressure that carbon dioxide formed by the reactiontaking place is substantially quantitatively taken up by the oxide ofcalcium under formation of carbonate of calcium.

5. A method according to claim 1, in which oxydic iron ore, solidcarbonaceous reducing agent and calcium oxide are caused to react atraised pressure in a closed vessel.

6. A method according to claim 4, in which oxydic iron ore, a mixture ofcarbon monoxide and hydrogen, and calcium oxide are caused to react atraised pressure in a closed vessel.

7. A method according to claim 1, in which a sulphidic ore, solidcarbonaceous reducing agent and calcium oxide are caused to react atraised pressure in a closed vessel.

8. A method according to claim 4 in which a sulphidic ore, a mixture ofcarbon monoxide and hydrogen, and calcium oxide are caused to react atraised pressure in a closed vessel.

9. A- method of producing metals from their ores consisting in heating amixture of ore, reducing agent containing the element carbon and calciumoxide to a temperature at which the reducing agent starts to reduce theore, bringing the mixture thus heated into a reaction chamber, closingsaid reaction chamber pressure tight, and allowing the reduction processto proceed by itself.

10. A method according to claim 9, in which the pressure developed bythe gases formed during the reaction is controlled by means of a valveon the reaction chamber.

11. A method of producing metals from their ores, in which the ore isheated in the presence of a reducing agent containing the element carbonand of calcium oxide at such pressure that carbon dioxide formed by thereaction taking place is substantially quantitatively taken up by theoxide of calcium under formation of carbonate of calcium, and where somefree oxygen is supplied to the mixture in the pressure chamber.

12. A method of producing iron from its ores consisting in making amixture of said ore with solid carbon, preheating said mixture,supplying hot calcium oxide thereto, transferring the mixture thusobtained to a pressure vessel, maintaining in said vessel 9. pressuresufllcient for the progress of the reduction of the ore, cooling thereaction mixture, and separating the iron from the other reactionproducts formed during the reduction.

13. A method of producing a magnetic metal from an ore thereof,consisting in heating the ore with calcium oxide and with reducing agentcon- 75 taining the element carbon under such pressure, that magneticmetal and carbonate of calcium are substantially quantitatively formed,and separating the metal from said carbonate over a magnetic separator.

14. A method of producing a magnetic metal from an ore thereof,consisting in treating the ore under pressure and heat together withcalcium oxide and with reducing agent containing the element carbon atsuch a pressure, that magnetic metal and carbonate of calcium issubstantially quantitatively formed, and separating the metal from saidcarbonate over a magnetic separator, and calcining the calcium carbonateto calcium oxide, using the calcium oxide thus obtained for repeatedoperation of the method.

15. A method of producing a metal from an ore thereoi. consisting ofheating the ore together with calcium oxide and with solid reducingagent containing the'element carbon and with a reducing gas, under suchpressure that metal and carbonate of calcium are substantiallyquantitatively formed, and separating the metal out of the reactionproduct.

16. A method according to claim 15, in which the reducing gas is carbonmonoxide.

17. A method according to claim 15, in which the reducing gas is amixture of carbon monoxide and hydrogen.

